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Science-based dietary recommendations: How much do we really know?

The authors of a key, highly-cited (close to 900 times) paper on bioactive compounds [1], report that numerous bioactive compounds discovered in fruit and vegetables appear to have positive effect on health:

Bioactive compounds are extranutritional constituents that typically occur in small quantities in foods. They are being intensively studied to evaluate their effects on health. The impetus sparking this scientific inquiry was the result of many epidemiologic studies that have shown protective effects of plant-based diets on cardiovascular disease (CVD) and cancer. Many bioactive compounds have been discovered.”

The authors emphasize that “Much scientific research needs to be conducted before we can begin to make science-based dietary recommendations” and note that the list of bioactive compounds is “ever-expanding“. Nevertheless, they conclude that

On the basis of a large population database, there is sufficient evidence to recommend a diet high in food sources rich in bioactive compounds”.

Interestingly, in another study, reporting the inhibition of colon and breast cancer cell proliferation by fruits and berries [2], we read that there exists “a synergistic effect of vitamin C and other substances” that may play an important role [emphasis mine].

So the compelling questions that emerge are: How many more different compounds and complex synergistic processes that link them exist? What does our lack of knowledge mean, practically speaking, in relation to the desirable concept of ‘sound nutritional advice’? Considering the complexity of the human body, is it possible to fully grasp the complete mechanism of nutrition through the studies performed in artificial laboratory environments?

Notably, the authors of a very recent publication citing [1], which reviews current evidence regarding the relationship between vegetarian eating patterns and cancer risk [3], report that

A vegan diet, aside from its deficit of vitamin B12 activity (readily compensated by supplementation), is typically more micronutrient-dense (per calorie) than the diets favored by omnivores

and

Fears that a vegan diet may be inadequate in protein quality or quantity are unfounded”.

Importantly, the authors emphasize that

a broad body of evidence links specific plant foods such as fruits and vegetables, plant constituents such as fiber, antioxidants and other phytochemicals, and achieving and maintaining a healthy weight to reduced risk of cancer diagnosis and recurrence”.

In conclusion, modern science may only begin to understand the full benefits of plant-based diets. It may take a lot of research to unravel the various pathways that lead to better health through nutrients-rich fresh fruit and veggies. Enough evidence indicates nevertheless that such diets may not only offer superior nutrition, but also reduce the chance of serious diseases through simple and achievable lifestyle choices.

Let us not waste time waiting until science figures it all out.

References:

[1] Kris-Etherton P.M., Hecker K.D., Bonanome A., Coval S.M., Binkoski A.E., Hilpert K.F., Griel A.E., Etherton T.D. Bioactive compounds in foods: Their role in the prevention of cardiovascular disease and cancer (2002) American Journal of Medicine, 113 (9 SUPPL. 2)

[2] Olsson M.E., Gustavsson K.-E., Andersson S., Nilsson A., Duan R.-D. Inhibition of cancer cell proliferation in vitro by fruit and berry extracts and correlations with antioxidant levels (2004) Journal of Agricultural and Food Chemistry, 52 (24) , pp. 7264-7271.

[3] Nagarathna Purada Kattimani Matada, Mukumbayi Mulumba Philippe, Raju Koneri. Department of Pharmacology, Karnataka College of Pharmacy, Bangalore, Karnataka, IndiaA Study on Plant Based Dietary Patterns and Cancer Risk (2013) Int. J. Pharm. Sci. Rev. Res., 23(2), Nov – Dec 2013; no 45, 265-278.

peaches from my garden

Standard human diet

There exist (at least) two alternative, competing philosophical concepts of probability.

One, more naive, is that real-life events are random, and so to model this, we use the probability theory to estimate the likelihood of their occurrence. As an example, when tossing a coin, we do not know whether we will obtain heads or tails. So we assume, for simplicity, that if the coin is symmetrical, then the chance of getting heads is the same as the chance of getting tails, and hence let the probability of observing either be 1/2.

The other, more insightful, is that real-life events are completely deterministic, and driven by the various factors contributing to those events. For example, when tossing a coin, whether we obtain heads or tails, completely depends on how we tossed the coin as well as the conditions of the surrounding environment. In particular, if all these factors were the same, we should observe the same outcome each time. Nevertheless, since there are too many factors for us to control them, it appears as if the outcomes of the tosses were random. So, for simplicity we make analogous modeling assumptions as in the fi rst case.

Whilst from the point of view of practical calculations, it does not matter which philosophical concept we adopt, as far as real-life is concerned, our approach may carry a tremendous amount of weight.

As one example of interest here, many have argued a range of views, often contradictory to one another, on what the natural human diet is and hence what the modern human diet should be, based on the history of human dietary patterns, going back in time thousands and even millions of years. A common line of reasoning used is that humans are predisposed to a particular way of eating, and won’t thrive unless they follow a particular diet that is being argued as the natural one. Such argument clearly contradicts the historical evidence of humans surviving in a multitude of di fferent, sometimes harsh conditions, thanks to adapting their eating habits to the range of foods available in those environments. Indeed, the major  flaw of such reasoning, is failing to see

  • that humans have a choice, which is constrained by the range of available options,
  • that the choice they make, results in outcomes, which include genetic changes, that in turn may affect future dietary preferences or digestive abilities, as well as
  • that there exist considerable individual differences in human needs and abilities, and that it is important for an individual to respond to those needs, in order to achieve best overall health and happiness outcomes.

So, although it would be convenient to assume that the world has made a choice for us, this may be a too naive, and too simpli ed model of the reality. The world may not be random, but it de nitely is very complex. Classifying diets may help, to some extent, in understanding of how it works, but cannot replace the reality or remove our freedom to choose what we desire and in doing so, change it. It could be more helpful perhaps, to see the world as the complex result of various actions and decisions, to which we may have some contribution, however small, than as a random outcome to which we have no say.

 

(extract from “Standard Human Diet: A stochastic modeller’s perspective”, Dr Gosia O’Reilly, draft)